The invention relates to a common rail injector for fuel injection in a common rail injection system of an internal combustion engine, which has an injector housing with a fuel inlet which communicates with a central high-pressure fuel reservoir outside the injector housing and communicates with a pressure chamber inside the injector housing from which highly pressurized fuel is injected depending on the position of a control valve which assures that a nozzle needle, which can move axially back and forth in a longitudinal bore in the injector housing counter to the initial stress of a nozzle spring, lifts up from a seat when the pressure in the pressure chamber is greater than the pressure in a control chamber, which can be connected by means of an inlet throttle to the fuel inlet and can be connected by means of an outlet throttle to a discharge chamber.
In common rail injection systems, a high-pressure pump feeds the fuel into the central high-pressure reservoir which is referred to as a common rail. High-pressure lines lead from the high-pressure reservoir to the individual injectors which are associated with the engine cylinders. The injectors are individually triggered by the engine electronics. The rail pressure prevails in the pressure chamber and at the control valve. When the control valve opens, the nozzle needle lifts up from its seat and highly pressurized fuel is injected into the combustion chamber of the engine.
In conventional injectors of the type disclosed, for example, by reference to German Patent No. 197 24 637 A1, the control chamber is disposed centrally in the injector housing, at the end of the longitudinal bore remote from the combustion chamber. The connection between the fuel inlet and the pressure chamber is produced by means of a bore that extends outside the longitudinal bore. This additional bore in the injector housing is subjected to the full rail pressure, at least during injection. As a result, insuring that the sealing of the injector housing occurs is quite a complex operation in terms of manufacturing engineering.
The principal object of the invention is to produce a common rail injector of the type described hereinbefore yet which has a simple design and is inexpensive to produce.
It is another object of the invention that the seal effectiveness should be improved.
In a common rail injector for the injection of fuel in a common rail injection system of an internal combustion engine, which has an injector housing with a fuel inlet which communicates with a central high-pressure fuel reservoir outside the injector housing and communicates with a pressure chamber inside the injector housing from which highly pressurized fuel is injected depending on the position of a control valve which assures that a nozzle needle, which can move axially back and forth in a longitudinal bore in the injector housing counter to the initial stress of a nozzle spring, lifts up from a seat when the pressure in the pressure chamber is greater than the pressure in a control chamber. The control chamber can be connected by means of an inlet throttle to the fuel inlet and can be connected by means of an outlet throttle to a discharge chamber so that the object of the invention is attained by virtue of the fact that the communication between the fuel inlet and the pressure chamber is disposed on the inside in relation to the control chamber. The design of the injector according to the invention is practically the reverse of the design of conventional injectors. By means of this measure, the high-pressure sealing of the injector housing is considerably simplified in terms of manufacturing engineering.
In one embodiment of the invention the nozzle needle has a central bore via which the fuel inlet communicates with the pressure chamber. The bore in the nozzle needle has the same function as the bore in the injector housing of conventional injectors. As a result of the embodiment of the injector according to the invention, the injector housing can be embodied [as] more compactly.
In another embodiment of the invention there is provided on the nozzle needle between the fuel inlet and the pressure chamber, at least one flat surface along which fuel can travel from the fuel inlet into the pressure chamber. This embodiment offers advantages particularly with regard to the high-pressure impermeability of the injector.
In yet another embodiment of the invention the central bore is an axial blind bore whose end communicates with the pressure chamber by means of at least one radial bore. If four radial bores extend out from the blind bore in a star shape, the highly pressurized fuel is distributed uniformly in the annular pressure chamber.
In still another embodiment of the invention the control chamber is disposed between the inner circumferential surface of the longitudinal bore and the outer circumferential surface of a sleeve, which can be slid in a sealed fashion onto the end of the nozzle needle remote from the combustion chamber and is held in contact with the injector housing with the aid of the nozzle spring. The sleeve provides a simple way of separating the control chamber from the fuel inlet.
In a further embodiment of the invention a biting edge is disposed on the surface of the sleeve which contacts the injector housing. This edge insures that the control chamber embodied outside the sleeve remains separate from the fuel inlet inside the sleeve in a pressure-tight manner.
In another embodiment of the invention the nozzle needle is guided between the control chamber and the pressure chamber. The nozzle needle of the injector according to the invention can be embodied as shorter than conventional nozzle needles. Therefore, a guide is required in order to assure a trouble-free operation of the injector.
In yet another embodiment of the invention the inlet throttle is integrated into the sleeve. The inlet throttle serves to prevent pressure surges during operation.
In still another embodiment of the invention the nozzle needle has a step embodied on it, which constitutes a stop for the nozzle spring. This design has the advantage that it is no longer necessary to provide a spring plate. This reduces the number of individual parts.
Yet another embodiment of the invention provides that the nozzle needle stroke is defined by the distance between injector housing and the end face of the nozzle needle remote from the combustion chamber. This embodiment has the advantage that it is particularly easy to produce in terms of manufacturing engineering.
Other advantages, features, and details of the invention ensue from the following description in which an exemplary embodiment of the invention is described in detail, with reference to the drawing. The features mentioned in the claims and the specification can be essential to the invention either individually or in arbitrary combinations with one another.